Rotational de-excitation of tricarbon monosulfide (C3S) in collision with (He): potential energy surface and rates

Abstract

Despite that the tricarbon monosulfide (C3S) is among the first sulfur-containing carbon-chain molecules to be detected in the interstellar medium, no studies focused on the determination of its collisional rates. These rate coefficients are essential to estimate the abundance of C3S in the interstellar medium. Computations of the C3S($^{1}\Sigma^{+}$ Σ + 1 ) downward rate coefficients, induced by collision with He, are performed by averaging the integral cross sections at low temperature (below $25~\text{K}$ 25 K ). Calculations of the cross sections in the close-coupling quantum time independent formalism for $E_{c}\leq110~\text{cm}^{-1}$ E c ≤ 110 cm − 1 and $J\leq10$ J ≤ 10 are based on a new 2-D potential energy surface. This PES is obtained from the explicit correlated coupled cluster with a single, double and perturbative triple excitation [ccsd(t)-f12] ab initio approach and the aug-cc-pVTZ basis sets. The PES have a global minimum of $-55.69~\text{cm}^{-1}$ − 55.69 cm − 1 located at $R=6.25$ R = 6.25 bohr and $\theta=94^{\circ}$ θ = 94 ∘ , and a second minimum of $-36.95~\text{cm}^{-1}$ − 36.95 cm − 1 at $R=9.35$ R = 9.35 bohr and $\theta=0^{\circ}$ θ = 0 ∘ . A comparison of C3S rates with those of the isoelectronic molecule C3O was made. The results indicate a great temperature dependence of the rates for transitions of $\Delta J>2$ Δ J > 2 . We expect that the new collisional data will allow for accurate determination of the C3S abundance in several interstellar regions.

BASECOL2023 scientific content

“…One recommended dataset is available for C 3 O and one for C 3 S. BASECOL2023 was updated with a dataset (Bop et al 2022b) for the rotational de-excitation of C 3 O by He (31 levels; T = 5-150 K) calculated with the PES of Khadri & Hammami (2019), and a dataset (Sahnoun et al 2020) for the rotational deexcitation of C 3 S by He (11 levels; T = 2-25 K); in the latter calculation the authors calculated a new PES.…”

The effect of scattering calculations on non-LTE modelling of the C3O and C5O abundances in TMC-1

“…Indeed, the C 5 O-He PES exhibits two minima of 59.3 cm −1 and 53.06 cm −1 which are similar in magnitude to the unique global minimum of 53.4 cm −1 obtained for C 3 O-He. Moreover, in C 𝑛 O-He (𝑛 = 3, 5) systems and unlike their C 𝑛 S-He valence isoelectronic counterparts (Sahnoun et al 2020;Khadri et al 2020), the charge distribution on the oxygen atom is negative and the Pauli exchange repulsion does not allow quasi-bonding between the O and He atoms. To check the validity of our new fit, we compare in Table 1 state-to-state inelastic cross-sections of C 3 O and C 5 O computed using the old (Khadri & Hammami 2019;Khadri et al 2022) and new (this work) analytical PESs.…”